getElementsByTagName vs selectNodes效率及兼容的selectNodes實現

更新時間：2010年02月26日 14:35:37 作者：

天在csdn上看到有人問 getElementsByTagName 和 selectNodes誰更快，這個還真沒研究過。

于是就測試了下：

 
var stringToDom=function(text) { 
var doc; 
if(window.ActiveXObject) { 
doc = new ActiveXObject("MSXML2.DOMDocument"); 
doc.loadXML(text).documentElement; 
} else { 
doc = (new DOMParser()).parseFromString(text,"text/xml"); 
} 
return doc; 
} 
var xmlDoc=stringToDom("<body><a href='a'>a</a><a href='b'>b</a></body>"), 
c, 
d1=new Date(); 
for(var i=0;i<100000;i++){ 
c=xmlDoc.getElementsByTagName("a"); 
} 
document.write("getElementsByTagName: ",new Date()-d1); 
d1=new Date(); 
try{ 
for(var i=0;i<100000;i++){ 
c=xmlDoc.selectNodes("a"); 
} 
document.write("<br/>selectNodes: ",new Date()-d1); 
}catch(ex){document.write("<br/>error:"+ex)} 

在IE下selectNodes還是快多了，
可以FF下卻沒有這個方法，google了下，找了方法，使用XPathEvaluator來實現，下面是具體實現，不過效率就不太理想了：

復制代碼代碼如下:

 
if (!window.ActiveXObject) { 
(function(){ 
var oEvaluator=new XPathEvaluator(),oResult; 
XMLDocument.prototype.selectNodes = function(sXPath) { 
oResult = oEvaluator.evaluate(sXPath, this, null, XPathResult.ORDERED_NODE_ITERATOR_TYPE, null); 
var aNodes = []; 
if (oResult != null) { 
var oElement = oResult.iterateNext(); 
while (oElement) { 
aNodes[aNodes.length]=oElement; 
oElement = oResult.iterateNext(); 
} 
} 
return aNodes; 
} 
})() 
} 

evaluate(xpathExpression, contextNode, namespaceResolver, resultType, result);
Returns an XPathResult based on an XPath expression and other given parameters.
xpathExpression is a string representing the XPath to be evaluated.
contextNode specifies the context node for the query (see the [http://www.w3.org/TR/xpath XPath specification). It's common to pass document as the context node.
namespaceResolver is a function that will be passed any namespace prefixes and should return a string representing the namespace URI associated with that prefix. It will be used to resolve prefixes within the XPath itself, so that they can be matched with the document. null is common for HTML documents or when no namespace prefixes are used.
resultType is an integer that corresponds to the type of result XPathResult to return. Use named constant properties, such as XPathResult.ANY_TYPE, of the XPathResult constructor, which correspond to integers from 0 to 9.
result is an existing XPathResult to use for the results. null is the most common and will create a new XPathResult
完整的測試頁面：

復制代碼代碼如下:

 
<!doctype HTML> 
<html> 
<head> 
<title>selectNodes&getElementsByTagName</title> 
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> 
<meta name="author" content="sohighthesky"/> 
<meta name="Keywords" content="selectNodes vs getElementsByTagName"/> 
</head> 
<body> 
</body> 
<script type="text/javascript"> 
/* 
*author:sohighthesky -- http://www.cnblogs.com/sohighthesky 
*content: selectNodes vs getElementsByTagName 
*/ 
if (!window.ActiveXObject) { 
(function(){ 
var oEvaluator=new XPathEvaluator(),oResult; 
XMLDocument.prototype.selectNodes = function(sXPath) { 
oResult = oEvaluator.evaluate(sXPath, this, null, XPathResult.ORDERED_NODE_ITERATOR_TYPE, null); 
var aNodes = []; 
if (oResult != null) { 
var oElement = oResult.iterateNext(); 
while (oElement) { 
aNodes[aNodes.length]=oElement; 
oElement = oResult.iterateNext(); 
} 
} 
return aNodes; 
} 
XMLDocument.prototype.selectSingleNode = function(sXPath) { 
oResult = oEvaluator.evaluate(sXPath, this, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null); 
// FIRST_ORDERED_NODE_TYPE returns the first match to the xpath. 
return oResult==null?null:oResult.singleNodeValue; 
} 
})() 
} 
var stringToDom=function(text) { 
var doc; 
if(window.ActiveXObject) { 
doc = new ActiveXObject("MSXML2.DOMDocument"); 
doc.loadXML(text).documentElement; 
} else { 
doc = (new DOMParser()).parseFromString(text,"text/xml"); 
} 
return doc; 
} 
var xmlDoc=stringToDom("<body><a href='a'>a</a><a href='b'>b</a></body>"), 
c, 
d1=new Date(); 
for(var i=0;i<100000;i++){ 
c=xmlDoc.getElementsByTagName("a"); 
} 
document.write("getElementsByTagName: ",new Date()-d1); 
d1=new Date(); 
try{ 
for(var i=0;i<100000;i++){ 
c=xmlDoc.selectNodes("a"); 
} 
document.write("<br/>selectNodes: ",new Date()-d1); 
}catch(ex){document.write("<br/>error:"+ex)} 
/* 
var n=xmlDoc.selectSingleNode("body/a"),doc=xmlDoc.selectSingleNode("body");//alert(n.childNodes[0].nodeValue) 
for(var i=0;i<10000;i++){ 
doc.appendChild(n.cloneNode(true)) 
} 
d1=new Date(); 
c=xmlDoc.getElementsByTagName("a"); 
document.write("<br/>getElementsByTagName: ",new Date()-d1); 
d1=new Date(); 
c=xmlDoc.selectNodes("a"); 
document.write("<br/>selectNodes: ",new Date()-d1); 
*/ 
</script> 
</html> 